64 Valiant power steering

Actually, the accurate steering box interchange is '62-'72 A- and B-body. If you have the money available, get a rebuilt & upgraded box from Firm Feel or Steer & Gear rather than going through the effort to swap in a loose and sloppy used box.

I am assuming your '64 has a slant-6 engine; if not, someone else will have to inform you about brackets and stuff. You can use the P/S pump and bracket from any slant-6; there were various types and styles used over the years. The only thing to watch for is if your '64 has air conditioning, you'll need a different pump pulley and bracket, and then your interchange might narrow down a little because not all the P/S brackets and pumps will clear the '64 A/C compressor + bracketry. Some P/S pumps use a 3/8" ID return hose and some use a larger 15/32" ID return hose; you may need to swap the return nozzle on the P/S box to match up with the return hose nipple on the P/S pump reservoir. Likewise, some P/S pressure hoses have a male-thread invert-flare fitting at the P/S box end, while others have a female. See here for details on how to work with that difference -- it's not difficult. You'll also need the P/S belt drive pulley that bolts onto the front of the crank pulley. They are all the same for all slant-6s. P/S and M/S pitman arms are identical for '62-'66 A-body; no other year or model interchanges on that part.